package threading;
class SingletonLazy{
    volatile private static SingletonLazy instance;
    public static SingletonLazy getInstance(){
        //这个条件，判定是否要加锁，如果对象已经有了，就不必加锁了，此时直接返回instance
        if(instance == null){
            synchronized (SingletonLazy.class){
                if(instance == null){
                    instance = new SingletonLazy();
                }
            }
        }
        return instance;
    }
    private SingletonLazy(){ }
}
public class ThreadDemo18 {
    public static void main(String[] args) {
       SingletonLazy s1 = SingletonLazy.getInstance();
       SingletonLazy s2 = SingletonLazy.getInstance();
        System.out.println(s1 == s2);
    }

}
